1. Field of the Invention
The present invention relates to a package board loaded with an integrated circuit (IC), and more particularly to a package board integrated with power supply for supplying electricity to the IC.
2. Description of the Related Art
Large-scale integrated circuits (LSIs) have been designed so as to reduce a drive voltage in order to achieve at one and the same time acceleration of velocity and lower consumption of electricity, and in recent years the drive voltage has dropped to near 1 V. To supply electricity to a LSI, the voltage of a power supply needs to be reduced before being supplied. A DC-DC converter using a switching device that ensures a high conversion efficiency is used, and a pulsating flow in the output of the switching device needs to be suppressed with a smoothing filter. This smoothing filter is constituted mainly of an inductor and a capacitor, and generally mounted on the surface as a discrete device. However, its mounting area can be expanded by mounting the inductor and capacitor in such a way that the mounting height is raised.
Prior Art 1 discloses a semiconductor device in which a board is provided with a noise-removing function. Prior Art 2 and Prior Art 3 disclose the structure of an inductance device. Prior Art 1: JP 10-233469 A is incorporated herein by reference. Prior Art 2: JP 7-201610 A is incorporated herein by reference. Prior Art 3: JP 7-263241 A is incorporated herein by reference.
With intensified performances and a lowering in the consumption of electricity in recent years, the drive voltage in a large scale integrated circuit device like a micro processing unit (MPU) has dropped to near 1 V so that, correspondingly, a current value has tended to rise significantly. On the other hand, fluctuations in voltage originating from components that are parasitic on wiring within a large scale integrated circuit produced for power supply and load becomes equal to a threshold voltage for driving a device in the large scale integrated circuit device. Occasions can thus occur when the large scale integrated, circuit malfunctions.
As a measure to counter fluctuations in voltage of power supply, demands have been made for the distance between the power supply and a load to be reduced as much as possible, and for this purpose it has been recognized that a very effective means to reduce the distance between the power supply and a load is to reduce the volume of the power supply itself as far as possible, so as to integrate the power supply with the package of the large scale integrated circuit device. However, it has become evident that a variety of problems can occur as a result of this. To cope with such problems, both the size and the height of the device within the power supply need to be reduced as much as possible, and, in particular, inductance has been a big factor in inhibiting reductions in the distance between the power supply and the load because it has tended to widen in order to meet with a situation that stems from a low level of voltage and a high level of current.